The present invention relates to a wire bonding apparatus, a bonding control program, and a bonding method for performing recovery processing after detecting non-bonding.
One of the assembly processes for semiconductors such as ICs (integrated circuits) is a wire bonding process for connecting between a semiconductor chip and a lead frame with wires.
In a typical wire bonding process, as seen from FIG. 15, pads 3 (first bonding points) of a semiconductor chip 2 and leads 4 (second bonding points) of a lead frame 15, both on a work 14, are connected by wires 12. FIG. 12 shows a structure of a conventional wire bonding apparatus, FIG. 13 is a flowchart of the bonding steps taken in this wire bonding apparatus, and FIG. 14 shows the bonding steps in conventional bonding process. This conventional wire bonding apparatus and process will be described below with reference to FIGS. 12 to 15.
In the wire bonding apparatus 100, as shown in FIG. 12, a bonding head 19 is set up on an XY table 20; and a bonding arm 13, moved in a Z direction by a motor, is provided on the bonding head 19; and in addition, a capillary 16 is attached to the tip end of the bonding arm 13.
The XY table 20 and the bonding head 19 make a moving mechanism 18. The moving mechanism 18, by the XY table 20, moves the bonding head 19 to any position in a horizontal plane (in the XY plane), and, by moving the bonding arm 13 attached thereto in the Z direction, the capillary 16 at the tip end of the bonding arm 13 is moved freely in the XYZ directions. A wire 12 is made to pass through the tip end of the bonding arm 13. The wire 12 is wound on a spool 11. To the wire 12 wound on the spool 11, an electrical conduction state acquisition device 22 is connected so as to acquire the electrical conduction state between the wire 12 and the work 14 by applying to and measuring electric current or electric voltage between the wire 12 and the work 14. To the bonding head 19, a clamper 17, that moves in the Z direction together with the capillary 16 and secures the wire 12, is attached so that it can freely open and close. To the bonding head 19, moreover, a position detection camera 128 for verifying the position of the semiconductor chip 2 is attached. Also, in the vicinity of the tip end of the wire 12, a ball formation device 26 (called electric torch or electric flame off probe) is attached for effecting electrical discharges between the wire 12 and forming a ball 5 at the tip end of the wire 12. The position detection camera 128 is connected to a position detection camera interface 140, the electrical conduction state acquisition device 22 is connected to an electrical conduction state acquisition device interface 42, the moving mechanism 18 is connected to a moving mechanism interface 44, and the ball formation device 26 (electric torch) are connected to a ball formation device interface 46. Each interface is in turn connected via a data bus 32 to a control section 30 within a computer 31 for controlling the wire bonding apparatus. To the data bus 32, furthermore, a memory unit 34 is connected for storing control data. The above-described wire bonding apparatus is disclosed in, for instance, Japanese Patent Application Unexamined Publication Disclosure No. 2003-163243.
The wire bonding apparatus 100 is controlled by the computer 31 and performs wire bonding with the following steps.                (1) The tip end of a wire 12 is formed into a ball 5 by the ball formation device 26, the position of the semiconductor chip 2 is detected by the position detection camera 128, and the capillary 16 is moved over a pad 3 (first bonding point) by the moving mechanism 18 (step S901 in FIG. 13, step (a) in FIG. 14).        (2) The capillary 16 is then caused to descend, and bonding is performed on the pad 3 (first bonding point) (step S902 in FIG. 13, step (b) in FIG. 14). The ball 5 is pressure-bonded on the pad 3 (first bonding point), so that a first bond portion 6 (pressure bonded ball) is formed.        (3) The moving mechanism 18 causes the capillary 16 to ascend from the pad 3 (first bonding point) and then moves the capillary 16 laterally (step S903 in FIG. 13, step (c) in FIG. 14).        (4) During the movement of the capillary 16, an electric current is made to flow from the wire 12 to the work 14 by the electrical conduction state acquisition device 22, and the electrical conduction state at that time is acquired by the electrical conduction state acquisition device 22. The acquired data are input to the control section 30 via the electrical conduction state acquisition device interface 42 (step S904 in FIG. 13, step (c) in FIG. 14). When the bonding to the pad 3 (first bonding point) is successful and bonding has been performed well, then an electric current is made to flow from the wire 12 to the work 14 in step (c).        (5) In the case of non-bonding (in the case that wire 12 is not bonded to the work 14), no first bond 6 is formed on the pad 3 (first bonding point), and the capillary 16 will ascend and move with the wire 12 at the tip end of the capillary 16 not connected to the pad 3 (first bonding point); as a result, no current will flow from the wire 12 to the work 14. It is thereby made possible to detect wire non-bonding. Acquired data on the electrical conduction state between the wire 12 and the work 14 are processed in the electrical non-bonding detection step by the control section 30, and whether non-bonding has occurred is determined (step S905 in FIG. 13, step (c′) in FIG. 14) (see Japanese Patent Application Unexamined Publication Disclosure Nos. H2 (1990)-298874 and H7 (1995)-94545, for instance).        (6) When it is determined in the electrical non-bonding detection step that non-bonding has occurred, the capillary 16 continues as before to move to a lead 4 (second bonding point), bonding is performed at the lead 4 (second bonding point), and, after causing the capillary 16 to ascend, the wire 12 is cut (steps S906 to S908 in FIG. 13). No electrical conduction state acquisition is, however, made for detecting a no-tail or lead non-bonding at the lead 4 (second bonding point).        (7) When wire cutting is finished, error processing is effected by a pad 3 (first bonding point) non-bonding signal, and the wire bonding apparatus 100 is stopped (step S909 in FIG. 13).        (8) Meanwhile, after bonding to the pad 3 (first bonding point), the moving mechanism 18 moves the capillary 16 to the lead 4 (second bonding point) and performs bonding at the lead 4 (second bonding point). If it is determined in the electrical non-bonding detection step that the pad 3 is not non-bonding (bonding on the pad 3 is successful), then when the capillary 16 is made to ascend thereafter, a current is made to flow from the wire 12 to the work 14 by the electrical conduction state acquisition device 22, and the electrical conduction state is acquired by the electrical conduction state acquisition device 22. When bonding to the lead 4 (second bonding point) is successful, and a tail wire 8 is formed properly at the tip end of the capillary 16, a current is able to flow from the wire 12 to the work 14. Conversely, if the wire 12 is accidentally cut while the capillary 16 is ascending, the current from the wire 12 to the work 14 will cease to flow. It is thus possible to detect whether or not the tail wire 8 is a no-tail in which the tail wire 8 fails to attain a prescribed length. Acquired data are input to the control section 30 via the electrical conduction state acquisition device interface 42 (steps S911 and S912 in FIG. 13, step (d) in FIG. 14 to steps (e) and (e′)).        (9) After the bonding to the lead 4 (second bonding point), the clamper 17 closes and ascends together with the capillary 16; and, as a result, the wire 12 is cut above a second bond 7 (step (e) to (f)). After this wire cutting also, a current will be made to flow from the wire 12 to the work 14 by the electrical conduction state acquisition device 22, and the electrical conduction state at that time will be acquired by the electrical conduction state acquisition device 22 (steps S913 and S914 in FIG. 13).        (10) If the bonding to the lead 4 (second bonding point) is successful and the cutting of the wire 12 is being properly effected, then when the capillary 16 is ascending, the current that was flowing from the wire 12 to the work 14 will have ceased to flow (step (f) in FIG. 14). When the cutting of the wire 12 is not being properly effected, on the other hand, as in the case that the wire 12 has been peeled away from the work 14, for example, the wire 12 will be electrically connected to the work 14 through the first bond 6, as shown in FIG. 14(f), as a result a current will flow. Moreover, when the current ceases to flow prior to the closing and ascending of the clamper 17, and no current is flowing even after the wire 12 is cut, even though the second bond 7 will have been formed, it will be possible to determine that there is a no-tail with the tail wire 8 not attaining the prescribed length. Thus, by processing the data output from the electrical conduction state acquisition device 22 in an electrical no-tail detection step in the computer 31, it is possible to determine whether the electrical conduction state after bonding to the lead 4 (second bonding point) is a no-tail or a lead non-bonding condition (steps S915 and S917 in FIG. 13) (see Japanese Patent Application Unexamined Publication Disclosure Nos. H2 (1990)-298874 and H7 (1995)-94545, for instance).        (11) When a no-tail or lead non-bonding is detected in the electrical no-tail detection step, by a signal therefrom, the wire bonding apparatus 100 performs error processing and stops (see Japanese Patent Application Laid-Open Disclosure H6 (1994)-5651, for example).        (12) When bonding to the lead 4 (second bonding point) has finished properly, the bonding cycle ends, and the capillary 16 is moved toward the next pad 3 (which is a next first bonding point).        
In the above description of the conventional art, wire non-bonding or no-tails are detected by processing signals from the electrical conduction state acquisition device 22 in the control section 30 of the computer 31 and, when it is determined thereby that a non-bonding or no-tail has occurred, then the wire bonding apparatus 100 is stopped. However, during a wire bonding process, various errors, in addition to what is described above, occur, such as the ball not being properly formed due to an electric discharge deficiency, when forming the ball 5 at the tip end of the wire 12 by electric discharge. In such cases also, conventionally, the wire bonding apparatus is stopped when a flaw is detected (see Japanese Patent Application Laid-Open Disclosure Nos. H6 (1994)-5651 and H3 (1991)-17376). Also, in view of the fact that there are cases where an error such as non-bonding or the like is caused when a ball 5 of the prescribed shape is not formed at the tip end of the capillary 16, methods have been proposed in which the wire bonding apparatus is stopped or an anomaly alarm is effected after imaging the shape of the tip end of that wire and processing the resulting data (see Japanese Patent Application Laid-Open Disclosure No. 2003-163243).
In the wire bonding apparatus 100 described in the above-referred art, despite the fact that various non-bonding detection device and methods are provided, when an error such as non-bonding is detected, nothing more is done besides stopping the wire bonding apparatus 100 or issuing a flaw alarm, and the apparatus does not process (correct) the error condition and continue bonding.
To the contrary, Japanese Patent Application Laid-Open Disclosure No. H6 (1994)-5651, for example, discloses that when it is determined by electrically detecting a discharge error that the tip end of the wire 12 is not formed in a prescribed ball shape, abandoning bond is performed at an unnecessary portion of the material being bonded, a ball is reformed, and then bonding is continued. However, with this method, unnecessary wire remains at the abandoning bond position, giving rise to the possibility of short-circuit, which is a problem.
Moreover, as to such errors as non-bonding in pad 3 (first bonding point) and lead 4 (second bonding point) and no-tail, since the situation at the tip end of the wire 12 varies, a simple recovery process such as the abandoning bond described above cannot be effected, and it will always be necessary to stop the whole bonding process and perform recovery process after an operator has verified the situation of the wire 12 and the like. Thus, it is not possible to recover from such errors and continue bonding.